The present invention relates to electrohydraulic control devices for double-acting consumers.
The invention is based on an electrohydraulic control device for a double-acting consumer. One such electrohydraulic control device is already known from European Patent Disclosure EP 0 110 126 A1, in which to control a double-acting consumer a longitudinally movable control slide can be actuated for a 4/3-way function of two magnets disposed oppositely on the housing. To keep the leakage slight, each consumer connection is secured in the manner of a seat valve by a hydraulically controlled blocking valve. The pilot control of these blocking valves is performed by those tappets that transmit the switching motion of the magnets to the control slide. Along with the functions of raising, holding and lowering, a fourth, free-float position can additionally be attained by briefly exciting both magnets at the same time. Moreover, the control device can also be used to control a single-acting consumer. A disadvantage of this control device, however, is that it works with magnets that merely switch, so that sensitive, proportional volumetric flow control is not possible. Moreover, the embodiment of the tappet as pilot control member makes for a relatively complicated structural design. The disposition of the switching magnets on opposite sides of the housing, in combination with the 4/3-way longitudinal slide and the tappets used for pilot control makes for a very long structure in the slide axis, which makes the control device unfavorable for mobile use.
An electrohydraulic control device is also known from German Patent Disclosure DE 41 40 604 A1; it works with a proportional magnet and is suitable for fine control of volumetric flows. The pilot control valve member disposed in a main valve member is actuated by the proportional magnet and cooperates like a followup controller with the main valve member, so that short response times and hence good regulating behavior are attained. The valve members for the main and pilot control stages are embodied as seat valves, which keeps the leakage slight. The control device is also embodied such that there is no need for a separate control oil supply. An unfavorable aspect of this control device is that it can execute only a 2/2-way function and is therefore unsuitable in this form for controlling a double-acting consumer.
It is an object of the present invention to provide an electrohydraulic control device for a double-acting consumer of the above-described type which avoids the above-described disadvantages.
According to the invention the electrohydraulic control device for a double-acting consumer includes
a first and second consumer connection, a first and second work conduit communicating with the first and second consumer connection respectively and including first and second blocking valves for blocking the consumer connections, a first lowering conduit communicating with the second consumer connection and a second lowering conduit communicating with the first consumer connection, each lowering conduit by-passing the blocking valves; and
electromagnetically actuable control means for blocking or connecting at least one consumer connection, which comprises a first four-way, two-position proportional magnet valve and a second four-way, two-position proportional magnet valve identical to the first four-way, two position proportional magnet valve. Each magnet valve includes a slidable valve member provided with control edges and having an initial position in which the connected work conduit is relieved, an inlet connection, a return connection, a first motor connection alternatively connected to the inlet connection or the return connection by operation of the slidable valve member with the control edges, a second motor connection and valve seat means for controlling, e.g. closing, the second motor connection. The first motor connection of the first magnet valve communicates with the first work conduit and the first motor connection of the second magnet valve communicates with the second work conduit. The second motor connection of the first magnet valve is connected with the first lowering conduit and thus the second consumer connection and the second motor connection of the second magnet valve is connected with the second lowering conduit and thus the first consumer connection.
The electrohydraulic control device according to the invention has the advantage over the prior art that while having a proportional mode of operation, it can control a double-acting consumer with little leakage. The magnet valves, because of the slide drives chosen, enable short response times, which leads to good regulating performance of the control device. The control device can attain a total of four work positions with only two magnets, so that in additional to the usual functions of raising, holding and lowering, a fourth, free-float position is possible by exciting both magnets; the switching sequence is arbitrary. The control device functions without a separate control oil supply and can moreover be used for a single-acting consumer. The control device is also compact in structure and is therefore suitable for mobile applications.
In preferred embodiments of the control device according to the invention used for regulating volumetric flow in each magnet valve the second motor connection is blocked by the seat valve means and the inlet connection is blocked by the slidable valve control member in its initial position and the slidable valve control member has a work position in which the inlet connection communicates with the first motor connection and the second motor connection communicates with the return connection.
Advantageously each slidable valve control member comprises a longitudinally movable main control member and each magnet valve comprises a pilot-controlled valve including the main control member, a proportional magnet and a pilot control member actuable by the proportional magnet to cooperate with the main control member so as to act as a followup controller. The seat valve means includes a main valve cone disposed on the main control member for blocking the second motor connection and is connected in series with a fine-control edge provided on the main control member for communication with the return connection and the control edges are disposed on the main control member spatially separated from each other.
In a particularly preferred embodiment the main control member has a thickened end portion having an end face defining an end-face pressure chamber adjoining the main control member so that a pressure in this pressure chamber urges the main control member in a closing direction. The pilot-controlled valve includes means for relieving the end-face pressure chamber including a slide edge, a pilot control cone connected in series with the slide edge, the slide edge and pilot control cone begin provided on the pilot control member, and a spring arranged to urge the pilot control member in a direction toward the initial position and opposite to another direction of motion of the pilot control member caused by operation of the proportional magnet. The main control member advantageously has at least one differential face and the main control member is urged in an opening direction by a pressure at the second motor connection acting on the at least one differential face. The main control member has a second differential face and is positionable so that a pressure at the inlet connection acts on the second differential face urging the main control member in an opening direction and the pilot-controlled valve includes means for connecting the end-face pressure chamber with the second motor connection or the inlet connection so that the end-face pressure chamber is selectively acted on by a higher pressure at the second motor connection or the inlet connection, and the means for connecting includes check valves and inlet throttles.
The pilot-controlled valve is provided with a slide bore for the main control member. This slid bore includes an inlet chamber, a first motor chamber, a return chamber, an intermediate chamber and a second motor chamber arranged in a preferred embodiment in succession spaced from each other in the slide bore with the inlet chamber being closest to the proportional magnet and the second motor chamber being furthest from the proportional magnet. The connections of the magnet valve are assigned to respective chambers of the slide bore.
In another embodiment of the control device the pilot-controlled valve advantageously includes a housing provided with slide bore through which the main control member is moved. This slide bore includes a return chamber, a second motor chamber, a first motor chamber, an inlet chamber and a magnetic-end pressure chamber arranged in succession with the magnet-end pressure chamber closest to the proportional magnet and the return chamber furthest from the proportional magnet. In this embodiment the main valve cone controls communication with the return chamber, a spring is provided in the return chamber and is arranged to urge the main control member towards the initial position and to press the main valve cone against a valve seat fixed in the housing of the pilot-controlled valve. The magnet-end pressure chamber is bounded by an end of the main control member closest to the proportional magnet so that pressure in the magnet-end pressure chamber urges the main control member in a direction toward a work position against action of the spring. The magnet-end pressure chamber is connected to the return connection via a throttle bore and is connected with the return connection by means of the pilot control member and the proportional magnet is provided with an armature and another spring braced against the housing and holding the pilot control member against the armature of the proportional magnet. Advantageously the main control member is provided with a throttle bore and a damping piston guided slidably in the throttle bore, protruding into the return chamber and provided with a return throttle. The first motor chamber is arranged side-by-side of the second motor chamber, the inlet chamber is located between the first motor chamber and the proportional magnet and an intermediate chamber is located between the second motor chamber and the return chamber.
According to a preferred embodiment the blocking valves each have an inlet-side inlet, a spring-loaded back end, a control connection communicating with the spring-loaded back end and means for transmitting a pressure prevailing at the inlet-side inlet of one blocking valve to the control connection of the other blocking valve and thus to the spring-loaded back end thereof so as to block the other blocking valve. Advantageously each blocking valve is provided with a throttle check valve and the control connections of both blocking valves communicate with each other for transmission of the pressure prevailing at the inlet-side inlet of one blocking valve to the spring-loaded back end of the other. This provides a reliable mode of operation and permits a space-saving, inexpensive structural design.
In one embodiment of the control device that can be used for an LS system the electromagnetically actuable control means includes an alternating valve which has a spring-centered middle position, is connected between the two first motor connections of both magnet valves and has two opposite end connections connected to the respective first motor connections and a middle connection connected to a load pressure line so that, when one end connection of the alternating valve is pressurized, a maximum pressure is transmitted into the load pressure line.
If the proportional magnets are arranged on one side of the housing of the control device, mechanical actuation is possible without major effort. This also results in a compact, space-saving design.
Valve seats are advantageously provided in the housing for the main valve members so that the control device can be manufactured economically.
The two blocking valves and the alternating valve are advantageously arranged in the housing in a region between the two magnet valves in various preferred embodiments. Particularly the magnet valves are arranged with their longitudinal axes in two planes parallel to each other and spaced from each other. The blocking valves are arranged axially parallel in the housing in different transverse planes spaced apart from each other and parallel to each other. The transverse planes are advantageously spaced apart a distance greater than a distance between the longitudinal planes in which the magnet valves are located. The location of the blocking valves in this embodiment leads to a space-saving structure and the resulting shortened conduits are also favorable for regulating performance.